1. Field of the Invention
The present invention relates to measuring apparatus such as instruments for measuring pH, oxidation-reduction potential, ion concentration, conductivity or the like of water, food and other samples.
2. Description of Related Art
Among so-called water quality measuring apparatus, there is a device which includes a detecting section which is operative to output a potential difference which can occur when a pair of electrodes are brought into contact with a test subject, and a main body operative to display a characteristic value, such as pH or the like, of the test subject determined from the potential difference as a measurement outcome. To enable a valid measurement with this apparatus, calibration needs to be accomplished in advance by using standard solutions wherein the pH values are known.
Since operations related to calibration can be relatively complicated as described in Japanese Patent Laid-Open Publication No. HEI 8-193990, and an incorrect calibration might be made because of mistaking a standard solution for another or following a wrong procedure if a person who is unfamiliar with or has poor knowledge of those operations is required to perform the calibration.
On the other hand, these types of measurements are often directly related closely to monitoring public health or are of particular interest from the viewpoint of the nature of a test subject for measurement and, hence, the outcome of measurement is required to have high reliability.
With conventional measuring apparatus, however, it is frequently difficult to check whether or not an accurate calibration has been made, and hence it is difficult to preclude errors in the measurement outputs due to an erroneous calibration. Therefore, such conventional apparatus cannot meet the data reliability requirement set forth in the FDA 21 CFR Part 11 (on electronic recording and electronic signature).
Accordingly, it is an object of the present invention to provide a measuring apparatus capable of checking upon, at least, the calibrator of the latest calibration at the time of measurement thereby making it easy to preclude measurement errors due to calibration made by an inept calibrator.